The invention relates to the cement manufacture and more specifically to clinker roasting plants.
The invention may be most advantageously used in the production of cement clinker in rotary kilns and it may also find application in chemical industry and ferrous and non-ferrous metal production where rotary kilns are employed.
A clinker roasting plant generally comprises a rotary kiln in which clinker is roasted and a hot head through which clinker is discharged from the rotary kiln.
Clinker is fed from the hot head to a cooler for cooling wherefrom the clinker is discharged as finished product.
Clinker is roasted in a rotary kiln by using burning fuel, such as fuel oil, gas and the like which is fed along a pipeline through the hot head of the kiln to the inner space of the rotary kiln housing.
Roasted clinker radiates much heat upon leaving the rotary kiln and during cooling in the cooler. This heat is used to heat the air cooling the clinker which is then directed to the kiln for fuel combustion. Thus, a major part of the heat emitted by hot clinker is utilized, but a substantial part of this heat is lost upon outburst of air from the cooler for cooling the clinker and during transportation of clinker.
Known in the art is a clinker roasting plant in which the heat radiated by clinker in the hot head of the kiln is utilized for heating fuel oil used as fuel for the kiln.
Preheating of fuel oil prior to burning is required for better combustion because the atomization of fuel is thus improved.
For that purpose, there is provided a heat exchanger in the form of a tubular coil surrounding a burner used for burning fuel oil. Fuel oil is positively fed to the coil to be heated up to a pre-set temperature and then fed to the burner.
This construction of the heat exchanger is explosion and fire hazardous due to direct contact of the coil with hot air-gas medium and to heat radiated by incandescent clinker. The coil-shaped heat exchanger does not provide for increase in the heat-exchange surface so that it is unsuitable for heating great quantity of water fed to the heat exchanger. It should be noted that assembly, disassembly, cleaning and other operations with the heat exchanger are also complicated because they can only be performed after suspension of kiln operation and its cooling.
Known in the art is a clinker roasting plant in which heat-exchange tubes are mounted to the inner side of the rotary kiln lining, and water circulates in the tubes. During operation of the kiln, a protective layer is formed which coats the inner side of the kiln walls and the tubes mounted thereto. This protective layer constitutes a protective coating preventing the heat-exchange tubes from wearing out.
This arrangement of the heat-exchange tubes permits, however, the water circulating therein to be heated at only 40.degree. C. This arrangement is almost unsuitable for utilization of heat of waste water because the tubes are rotated together with the kiln so that it is impossible to sealingly feed the flows of outcoming water to an external heat supply piping system which operates at relatively high pressure of up to 12 atm. In case of breakage of the protective coating at some portions of the tubes the bare tubes may burn through, and feeding of great quantity of water to the kiln in such case may result in a blow-up.
It is also known to use heat-exchange tubes which are accommodated in the inner space of a clinker cooler, e.g. secured to the side walls. The tubes may be of any configuration, such as in the form of a coil. A coolant is fed to the tubes for taking off the heat and for cooling the clinker. Water is generally used as coolant.
The tubes are arranged in difficulty accessible places in the inner space of the clinker cooler so that their inspection and repair are complicated. In addition, they are prone to an intensive wear and dust deposit so that their heat-exchange capacity is impaired.
Inspection, assembly, disassembly and repair of the tubes cannot be made without suspending operation of the kiln and clinker cooler.
A short-time interruption of water circulation in the tubes may result in burning through of the heat-exchange tubes.
A common disadvantage of the prior art plants resides in the fact that in cases hot water is not required, such as during summer period when water is not fed to heat exchangers, the heat-exchange tubes are burnt through and become unsuitable for operation.